Outlook calendars getting mixed up

Hi, 

   I have multiple emails (office365, gmail, yahoo etc) configured in my outlook. A few of them are business and others are personal ids. Office 365 email ids are business email ids, which respective business domains.

       Off lately, I have observed that any meeting invite being sent on a personal gmail id (say, email address removed for privacy reasons), gets added into the calendar of a business O365 email id (say, email address removed for privacy reasons). I am not sure if my business calendar could be seen by my colleagues or not, but still, I would not like to get my appointments mixed up like above. 

Any thoughts on why are they getting mixed up and what could be done to sort this out ? 

Thx, 

Nk